Alloy metal film resistor



y 1948. J. w. JlRA 2,440,691

ALLOY METAL FILM RESISTOR Filed March 7, 1945' FigJO \35 as INV TOR E34 g 9 34:? 84 9 w.

'ow a wm.

Patented May 4, 1948 UNITED STATES PATENT OFFICE ALLOY METAL FILM RESISTOR Joseph W. Jira, Newburgh Heights, Ohio, assignor to Continental Carbon, Inc., a corporation of Ohio Application March 7, 1945, Serial No. 581,545 17 Claims. (Cl. 201-76) My invention relates in general to resistance units and heating units, and more particularly to precision resistance units and heating units employing a thin film on a nonconductive carrier. However, for the sake of expediency and clearness the following description will be made with reference to a precision resistance unit, but will be understood to include resistance heating units as well.

The basic conception of applying a thin metallic film upon a nonconductive carrier to serve as a resistance unit, has long been known, Although metal itself is well known for its good conductive properties, it is applied in such exceedingly thin coating, that in fact only a limited amount of electricity can be conducted thereby, and the unit therefore, serves effectively as a resistor. However, it has been exceedingly difficult to obtain a continuous metallic film of suitably thin dimensions which would adhere properly to the carrier, be evenly dispersed, and resist deterioration during use. Further, methods which are known today for applying thin metallic film to a non-conductiv carrier are expensive, difiicult to control, and in particular are not adapted to producing a resistance unit of a relatively low ohmic value without transgressing the boundary and becoming a conductor i. e. offering exceedingly low fractional ohmic resistance values.

Therefore, an object of my invention is to construct a metallic film resistance unit possessing all the qualifications of a precision resistor,

Another object of my invention is to construct a resistance element by automatically depositing a thin alloy film of metal upon the surface of a non-conductive carrier,

Another object of my invention is to construct a resistance element by coating a non-conductive carrier with a mixture of two or more thermally decomposable metallic compounds and heating same to atomically deposit a thin'alloy film of the metals upon the non-conductive carrier and to drive off and remove the residual decomposition products.

Another object of m invention is to provide a method of controlling the thickness of the thin metal alloy film deposited upon the non-conductive carrier.

Another object of my invention is to provide a resistance unit employing a thin alloy film of metal upon the surface of a non-conductive carrier which has an ohmic resistance from a fraction of an ohm to a value, running into several hundreds of ohms.

Another object of my invention is the method 2 for constructing a low ohmic value metallic alloy resistance unit in which the temperatui'e coefficient of resistance may be controlled by the selection of the percentages of the various metals constituting the thin alloy film.

Another object of my invention is the method of producing a resistance unit of a thin alloy film upon a non-conductive carrier by the selection of at least two metals to be deposited on the non-conductive carrier which will form an alloy in order that higher processing temperatures may be used without driving off the metal of the film and causing discontinuities to raise the resistance of the unit.

Other objects and a fuller understanding of my invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings, in which:

Figure 1 shows a longitudinal view of the resistance unit embodying the features of my invention, partly in section along the lines |-i of Figure 8;

Figures 2 to 8 inclusive, show the steps by which my improved alloy resistor is constructed, the Figure 8 being a section taken transversely to the terminal connection;

Figure 9 is a side elevational view of a plate type resistor which may be used as a heating element; and

Figure 10 is a cross-sectional view taken along the line l0l 0 of Figure 9.

With reference to the Figure 1, my resistance 'unit comprises a non-conductive carrier H], a

thin metal alloy film ll deposited upon the outer surface of the non-conductive carrier I ll, a body of thin metal deposit l2 upon each end portion of the thin metal alloy film I l and a terminal member i3 having a lead l4 connected to the body of the thin metal deposit 12 upon each end of the resistor.

The non-conductive carrier in may be constructed of any suitable material and may comprise a rod or a hollow tube as shown in Figure 2 and be made of ceramic material which will withstand thermal shock and which possesses a very low moisture absorbing characteristic. In actual practice, I find that a ceramic material like Isolantite or its equivalent is suitable and preferable for resistors. A material that will withstand thermal shock and stand up under high temperature is required for units used for heating.

The thin metal alloy film H is atomically deposited upon the outer surface of a non-conductive carrier 10 by coating the outer surface with a'mixture of. at. least. two organo-compounds of a substantially stable and substantially non-oxidizable metal and heating the same. By non-oxidizable metal is meant a metal which is normally resistant to oxidation at a temperature which is suificient to cause the rapid oxidation of carbonaceous materials. Before applying the organo-compound mixture to the ceramic tube III, the outer surface is subjected to a degreasing or cleaning operation. This may be done by the suspending or immersing of the ceramic tube in a solution containing 50% carbon tetrachloride and 50% ethylene dichloride by volume, or a boiling solution of trisodium phosphate may be used, and the tube suspended therein for approximately ten minutes. Thereafter, the non-conductive carrier is permitted to air dry before being subjected to the film forming operation. It is understood of course, that numerous other chemical cleaning agents are adapted for use in the cleaning operation and the foregoing are cited only by way of example. It is usually necessary to wash the ceramic tubes five or six times in clear running water before drying in order to remove excess cleansing solution. Upon the drying of the ceramic tube 10, a thin coating of the mixture of organo-compounds comprising organic resinates of stable and substantially non-oxidizable metals is applied to the ceramic tube by either dipping, brushing or spraying. The term substantially stable and substantially non-oxidizable metal comprises those metals principally of the noble group although not limited thereto. The metal must remain substantially stable and be substantially non-oxidizable under high temperatures suficient to burn out any residue or decomposition products remaining after the decomposition of the metal upon the ceramic tube. Under the general class of compounds known as the resinates, are included the constituents of natural occurring resinates, resin exudations from trees, and synthetic preparations. In preparing my metallic organo-compounds for the mixture, the metal is substituted into or added to the organo-resinate. f the metals, I find that palladium, platinum, gold and silver are among the metals which may be substituted into or added to the resinate giving the respective metal resinate. My invention will hereinafter be described in connection with gold and palladium resinate but it will be understood that it includes similar stable and non-oxidizable metals or equivalents. Also, my invention is broad enough in scope to include other types of compounds which may not be organic in nature, and which may result in volatile decomposition products, or decomposition products of a nature other than that of being carbonaceous.

The resistance for a definite size resistor as produced by this invention is lower than that produced by my Patent No, 2,281,843. The low ohmic values are produced in this invention by the combination of physical properties of two metals, in this illustrationgold and palladium. It is found that by combining gold and palladium resinate in such proportions as would produce an alloy film containing 72% gold and 28% palladium as an example, the resistance obtained was between .05 ohm and .1 ohm when the film was deposited on a ceramic tube one inch long and of an inch in diameter. Whereas, for the same size tube, palladium gave a minimum value of substantially 1000 ohms and platinum gave a minimum value of substantially ohms. Even with very careful work, gold was found to be very difficult to apply to the carrier, and a minimum value of 5 ohms was obtained. The reason for the minimum values does not seem to be the same for all metals. In the case of gold which is a highly non-oxidizable material, it was found that temperatures usedto burn off the residual carbonaceous material vaporized portions of the extremely thin atomic deposit of gold. Therefore, discontinuities were encountered which tend to increase the ohmic value of a gold resistor high above the value which it shouldobtain. On the other hand, palladium is found to oxidize to a certain percentage of the total palladium present, and tends to reach an equilibrium at that point. Therefore, when using palladium on a carrier, an extremely low ohmic value could not be obtained because of this described equilibrium. However, palladium normally has a high vapor pressure at the processing temperatures and therefore, does not tend to vaporize from the carrier. The direct interaction between two alloyable materials, as set forth herein, appear to stabilize one another and produces highly desirable effects.

Another very desirable feature accomplished by the alloying of two metals having different properties, is the control of the temperature coemcient of resistance.- Resistors made with pure gold film are found to have a high positive temperature coeflicient of resistance. On the other hand, when making resistors of palladium film, it is found that with an increase in the amount of palladium, as before described, an increase in the amount of oxide of palladium is formed. This oxide of palladium is found to produce a high negative temperature coefiicient of resistance. Therefore, by the variation of the amount of palladium and gold in the alloy film, the negative and positive coefficient of resistance can be balanced one against the other to produce a resistor having exactly the desired amount of temperature coefficient.

By varying the percentage of gold in the alloy of this example, from substantially 1% to substantially 99% of the total, it was found that the temperature coefiicient of resistance could be controlled within a range from substantially minus 5% to substantially positive 5% of the zero temperature coefficient of resistance.

It is difiicult to obtain a commercially feasible resistor by applying a substantially saturated mixture of the metallic resinate, without an appropriate carrier or thinner, to the ceramic carrier. Even though attempts to apply by brushing or dipping a substantially saturated mixture of the resinate, in the absence of a thinner, as thinly as possible upon the carrier, yet the atomically deposited metallic alloy film results in too great a thickness to give the desired ohmic value of resistance. A thinner functions as a medium for carrying the resinate, so that the said resinates are evenly distributed or dispersed in an even coating upon the ceramic carrier l0. That is to say, the organoresinates are usually dispersed in the carrier or thinner, and when applied to the ceramic carrier gives in effect, a reduced amount of the metal. 0f the suitable thinners, I find that a compounded thinner as disclosed in my application for Letters Patent filed concurrently herewith, entitled Thinner for organoresinate is quite satisfactory. This thinner (or solvent as the case may be) is comprised substantially of two relatively high boiling ketones coupled by an intermediate agent, and supplemented by a tacky oxidizable material. Namely, the thinner is comprised of from 5% to 20% acetophenone, 10% to will not be bonded thereto as-one continuous film, but will have many interruptions in the continuity thereof which tend to cause a higher value of resistance. Therefore,

After the coating comprising the mixture of resinates and the thinner, which is represented by the reference character 20, in Figure 3, is aprier. The precipitation of the pure metals from the resinate mixture starts at temperatures ranging anywhere from approximately 200 centigrade to 400 centigrade. The time was found tovary thickness of the applied coating. When using organo-resinates, the precipitation of the metals tated metal tightly to the carrier.

The second stage heating is to completely oxidize the ash or residue and to drive off any volatile decomposition products as well as to insure a complete precipitation of the virgin metals. heating may range from 400 centigrade 120750" centigrade for about one hour.

The Figure shows the ceramic tube after the residue is thoroughly oxidized and removed by volatilization to leave the thin alloy film I I which may be characterized as the basic resistance. The metallic film possesses unusually good bonding properties. In fact, the metalbonding characteristic is such that the only means of removal from the ceramic carrier is by grinding. The ceramic and the deposited metals are virtually one.

The next general series of steps in my process is to connect the terminal members l3 having leads ll to the end portions of the thin metal film H. To do this, I first deposit a, body of thin metal I 2 upon the end portions of the alloy film II as shown in Figures 1 and 7. The body of the thin metal l2 maybe physically deposited upon the end portions of the alloy film H by coating theend portions with a band of colloidal silver 7 plied on top of the example, the general as indicated by the reference character 22 in Figure 6 and heating the same at approximately 500 "centigrade to 600 centig'rade for 30 minutes or thereabouts.

Figures 1 and 8, making a good electrical contact with the silver. The terminal members 13 terminal members [3 together. at the rivet may also be soldered.

The silver is ideally process since it The connection will produce a 10,000 ohms. Therefore, by utilizing five or six basic values a great number of various resistance values are possible. The resistor is then given a coat of moisture-proof lacquer which when dried completes the process. In my invention, the heating to burn out the ash Or residue is below the melting point of the precipitated metal and also below the oxidizing temperature of the metal, giving a good stable and continuous film.

The initial basic resistance value of the alloy film I i may be controlled by the number of coats applied to the ceramic carrier or by varying the amount of the metallic resinates in the applied coating. In the event an additional number of coatings are applied, they may be added at difierent stages in the process. the additional coatings may beapplied on top of the coating 20 in Figure 3, after each applied coating is allowed to dry. After the several coat ings are dried, the process is then carried out as above explained. As a second example, an additional coating may be applied on top of thecoating 2| in Figure 4, which means that two first stage and one second stage firings are required. Under the second example, any number of coatings may be applied by repeating the procedure. After the additional coatings have been added under the second example, the general process is then completed as previously described. As a third example, an additional coating may be apmetal film H in Figure 5, which means that two first stage and two second stage firings are required. Under the third example, any number of coatings may be applied by repeating the procedure. After the additional coatings have been added under the third process is then completed as previously described.

With reference to the Figure 9, I illustrate a substantially fiat plate unit, which maybe made by my improved method. TheFigure 10 is a cross-sectional view taken along the lines Ill-I0 of Figure 9. In tion, the figure ill indicates a substantially fiat plate non-conductive carrier having a thin metallic alloy coating 3| thereon. Although the coating 3| is illustrated as being on both sides of the carrier 30, it is understood that this coating may be placed on only one side thereof if desired. A body of thin metal deposit 32 is placed upon each end portion of the metal alloy film 3i, and terminal members 33 having lead wires 34 are connected to the body of the thin metal deposit 32 upon each end of the unit. In all respects, the method of producing a unit of this type is substantially similar to that described in connection with the tubular type. It has been found, that a construction of the type illustrated in Figure 9 is suitable for a resistance unit or as a heating unit. When properly constructed, this plate type unit was found to radiate suflicient heat to serve as a toaster unit, or as a heater unit. However, it is not essential to provide leads as described. The unit may be provided to insert into suitable clips if desired.

Due to the fact that the conducting medium of my invention is metal, many of the difllculties arising from the use of carbon were completely eliminated. The first of these deficiencies was temperature coefllcient of. resistance. It is well known that carbon possesses a negative temperature coefllcient, a factor partly responsible for resistor failures when subject to normal or twice rated wattage.

Since gas carbon is now chiefly employed in carbon composition type resistors, it exerts a certain amount of influence upon the water repellency of the manufactured unit. Since gas carbon is hygroscopic it prevents the manufacture of a resistor possessing a stable shelf life or a low humidity characteristic, even if thoroughly impregnated in wax under reduced pressure.

Furthermore, since the conventional carbon composition resistor is an admixture of carbon and a bonding agent, usually a polymerizable resin, it is more or less prone to carbonization and therefore deterioration while under the influence of heat, a factor chiefly responsible for resistor failure.

By virtue of the bonding medium and countless particles of carbon that do not contribute towards the resistance value (undispersible conductor) hundreds of minute capacities are formed which exert a pronounced influence upon the high frequency characteristic of the unit.

All the above shortcomings of the carbon type resistor were completely rectified by the metal film resistor.

The new resistor not only possessed all the desirable electrical characteristics of a wire wound unit, but for a given value and wattage rating was one-tenth the size, a factor of commercial importance.

The most diflicult steps encountered in fabricating a resistor of the type were the following:

(1) The applied metallic organo-fllm had to be evenly distributed over the surface of the carrier, otherwise areas of uneven density appeared over the periphery of the unit and caused erratic resistance fluctuations during the spiralling operation.

(2) Temperatures had to be carefully controlled otherwise nonadhering or only partly adhering metallic films resulted.

(3) The deposited metallic film it had to be of sufficient thickness to prevent discontinuous electrical paths resulting from a difference in the this embodiment of my inventially a linear coefficients of expansion of the metal fllm and the ceramic carrier.

(4) Holding the deposited metallic flakes in place until bonded to the carrier.

(5) The control of the temperature coefllicient of resistance.

While I have described my invention with reference to resistance units and heaters, it is essencurrent conducting element and is not limited in scope to resistance units and heaters as commonly defined in the commercial industry.

Although I have described my invention with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

I claim as my invention:

1. The process of constructing a, metallic film on a non-conductive carrier, comprising providing a mixture of at least two metallic organocompound resinates of substantially stable and non-oxidizable alloyable metals, adding a thinner to the mixture to evenly distribute said resinates, said thinner comprising substantially 5% to 20% acetophenone; 10% to 25% nitrobenzene; 10% to 30% fenchone; and the remainder being a compound selected from the class consisting of pinene or turpentine, coating the non-conductive carrier with the thinned mixture, drying the coated carrier, and thereafter heating same to decompose the organoresinates and precipitate the metals therefrom as an alloy upon the nonconductive carrier and to remove any carbonaceous residue remaining after said precipitation.

2. The process of constructing a metallic film on a non-conductive carrier comprising providing a mixture of at least two thermally decomposable compounds of substantially stable and nonoxidizable metals which are alloyable with one another, saiddecomposable compounds being decomposable to the extent of precipitating the virgin metal therefrom, adding a thinner to the mixture to evenly distribute same, coating the said carrier with the thinned mixture, drying the coating thereon, thereafter heating said coating to decompose said decomposable compounds and deposit said metals as an alloy film upon the said carrier, and thereafter heating said coating to remove and driveoff any residual decomposition products.

3. The process of constructing a metallic film on a non-conductive carrier, comprising providing a. mixture of thermally decomposable compounds of substantially stable and non-oxidizable metals, said mixture of compounds containing at least one thermally decomposable compound of gold and at least one thermally decomposable compound of palladium, said decomposable compounds being decomposable to the extent of precipitating the virgin gold and the virgin palladium therefrom, adding a thinner to the mixture to evenly distribute same, coating the said carrier with the thinned mixture, drying the coating thereon, thereafter heating said coating to decompose said decomposable compounds and deposit the said gold and the said palladium as an alloy film upon the said carrier, and thereafter heating said coating to remove and drive off any residue decomposition products.

4. The process of constructing a metallic film on a non-conductive carrier, comprising providing a mixture of thermally decomposable com- 'ture to evenly distribute 9 pounds of substantially stable and non-oxldizable metals, said'mlxture of compounds containing at least one thermally decomposable compound of gold and at least onethermally decomposable compound of palladium said decomposable compounds being decomposable to the extent of precipitatin'g the virgin gold and the virgin palladium therefrom, adding a thinner to the mixsame, coating the said carrier with the thinned mixture, heating the coated non-conductive carrier to first thermally decompose the said decomposable compounds and deposit a t alloy film of the gold and palladium upon the non-conductive carrier and to secondly remove and drive off any residual decomposition products, and providing suitable terminals to connect with the said thin alloy film.

5. The process of constructing a metallic film on a non-conductive carrier, comprising providing a mixture of thermally decomposable compounds of ubstantially stable and non-oxidizable metals, said mixture of compounds containing at least one thermally decomposable compound of gold and at least one thermally decomposable compound of palladium, said decomposable com pounds being decomposable to the extent of precipitating the virgin gold and the virgin palladium therefrom, adding a thinner mixture, drying the coating thereon, thereafter heating said coating substantially within a range of temperature between 200 centigrade and 400 centigrade to decompose said decomposable compounds and deposit the said gold and the said palladium as an alloy film upon the said carrier, and thereafter heating said coating substantially within a range of temperature between 400 centigrade and 750 centigrade to remove and drive off any residual decomposition products.

6. The process of constructing a metallic film on a non-conductive carrier, comprising providing a mixture of at least two metallic organo-compound resinates of substantially stable and nonoxidizable alloyable metals, coating the nonconductive carrier with the mixture, drying the coated carrierand thereafter heating same to decompose the organoresinates and precipitate the metals therefrom as an alloy upon the non-conductive carrier and to remove any carbonaceous residue remaining after said precipitation.

7. The process of constructing a metallic film on a nonconductive carrier comprising providing a mixture of at least two thermally decomposable compounds of substantially stable and non-oxidizable metals which are alloyable with one another, said decomposable compounds being decomposable to the extent of precipitating the virgin metal therefrom, coating the said carrier with the mixture, drying the, coating thereon, thereafter heating said coating to decompose said decomposable compounds and deposit said metals as an alloy film upon the said carrier, and thereaiter heating said coating to remove and drive oil any residual decomposition products.

8: The process of constructing a metallic film on a non-conductive carrier, comprising providing a mixture of thermally decomposable compounds of substantially stable and non-oxidiza ble metals, said mixture of compounds containing at least one thermally decomposable compound of gold and at least one thermally decomposable compound of palladium, said decomposable compounds being decomposable to the extent of precipitating the virgin gold and the virgin palladium therefrom, coating the said carrier with the mixture, drying the .coating ing a mixture of thermally decomposable compounds of substantially stable and non-oxidizable metals, said mixture of compounds containing at least one thermally decomposable compound of gold and at least one thermally decomposable compound of palladium, said decomposable compounds being decomposable to the extent of precipitating the virgin gold and the virgin palladium therefrom, coating the said carrier with the mixture, heating the coated non-conductive carrier to first thermally decompose the said decomposable compoimds and deposit a thin alloy him of the gold and palladium upon the non-conductive carrier and to secondly remove and drive on any residual decomposition, and providing suitable terminals to connect with the said thin alloy film 10. The process of constructing a metallic film on a non-conductive carrier, comprising providing a mixture of thermally decomposable compounds of substantially stable and non-oxidizable metals, said mixture of compounds containing at least one thermally decomposable compound of gold and at least one thermally decomposable compound of palladium, said decomposable compounds being decomposable to the extent oi precipitating the virgin gold and the virgin palladium therefrom, adding a thinner to the mixture to reduce the concentration of the gold and pailadium, coating the said carrier with the thinned mixture, drying the coating thereon, thereafter heating said coating substantially within a range of temperature between 200 centigrade and 400 centigrade to decompose said decomposable compounds and deposit the said gold and the said palladium as an alloy film upon the said carrier, and thereafter heating said coating substantially within a range oi temperature between 400 ecutigrade and 750 centigrade to remove and drive ofi any residual decomposition products.

11. Zhe process of constructing a metallic film on a non-conductive carrier, comprising providing a mixture of thermally decomposable compounds Of substantially stable and non-oxidizable metals, said mixture of compounds containing at least one thermally decomposable compound of gold and at least one thermally decomposable compound of palladium, said decomposable compounds being decomposable to the extent of precipitating the virgin gold and the virgin palladium therefrom, adding a thinner to the mixture to reduce the concentration of the gold and palladium therein to substantially 1%, coating the said carrier with the thinned mixture, drying the coating thereon, thereafter heating said coating substantially within a range of temperature between 200 centigrade and 400 centigrade to decompose said decomposable compounds, and deposit the said gold and the said palladium as an alloy film upon the said carrier, and thereafter heating said coat' g substantially within a range or temperature between 400 centigrade and 750 centigrade to decompose said 11* centigrade to remove and drive 01! any residual decomposition products.

12. The process of constructing a metallic fi-lm on a non-conductive carrier, comprising providing a mixture of thermally decomposable compounds of substantially stable and non-oxidizable meta1, said mixture of compounds containing at least one thermally decomposable compound of gold and at least one thermally decomposable compound of palladium, said decomposable compounds being decomposable to the extent of precipitating the virgin gold and the virgin palladium therefrom, adding a thinner to the mixture to evenly distribute same and reduce the concentration of the gold and palladium, coating the said carrier with the thinned mixture, drying the coating thereon, thereafter heating said coating substantially within a range of temperature between 200" centigrade and 400 centigrade for a period of in a range from15 to 30 minutes to decompose said decomposable compounds and deposit the said gold and the said palladium as an alloy film upon the said carrier, and thereafter heating said coating substantially within a range of temperature'between 400 centigrade and 750 centigrade for a period of time of substantially one hour to remove and drive off any residual decomposition products.

13. The process of constructing a metallic film on a non-conductive carrier, comprising providing a mixture of thermally decomposable compounds of substantially stable and non-oxidizable metals, said mixture of compounds contalning at least one thermally decomposable compound of gold and at least one thermally decomposable compound of palladium, said decomposable compounds being decomposable to the extent of precipitating the virgin gold and the virgin palladium therefrom, adding a thinner to the mixture to evenly distribute same, coatin the said carrier with the thinned mixture, heating the coated non-conductive carrier to first thermally decompose the said decomposable compounds and deposit a thin alloy film of the gold and palladium upon the nonconductive carrier and to secondly remove and drive ofi any residual decomposition products other than said alloy film, said heating being below the temperature at which the vapor pressure of said alloy film becomes equal to the atmospheric pressure.

14. An article of manufacture comprising a non-conductive carrier, an alloy film of at least two substantially stable and non-oxidizable metals tightly bonded to said carrier, and electrical terminal means for said alloy film.

15. An article of manufacture comprising a non-conductive carrier having a tightly bonded conductive film thereon, said film comprising an alloy of at least two materials, one of said at least two materials having a positive coefliclent of resistancefand the other of said at least-two materials having a negative coefiicient of resistance, said materials being proportioned in said alloy to produce a resultant coefiicient of resistance of a predetermined value.

16. A current conducting article comprising an alloy of at least two materials, one of said at least two materials having a positive coefiicient of resistance, and the other of said at least two materials having a negative coefficient of resistance, said materials being proportioned in said alloy to produce a resultant coeflicient of resistance of a predetermined value in a. range of plus and minus 5% of the zero temperature coefiicient of resistance.

17. The process of constructing a metallic film on a non-conductive carrier, comprising selecting at least one compound from the group including thermally decomposable compounds of metals that are substantially stable and nonoxidizable and having a positive coefficient of resistance, selecting at least one compound from the group including thermally decomposable compounds of metals that are substantially stable and non-oxidizable but forms upon heating a small amount of oxide which has a negative coefiicient of resistance, said decomposable compounds being decomposable to the extent of precipitating the virgin metal therefrom, mixing the said decomposable compounds, adding a thinner to the mixture to evenly distribute same, coating the said carrier with the thinned mixture, drying the coating thereon, thereafter heating said coating to decompose said decomposable compounds and deposit said metals as an alloy film upon the said carrier, and thereafter heating said coating to remove and drive off any residual decomposition products.

JOSEPH W. JIRA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,896,193 Corson Feb. 7, 1933 2,281,843 Jira May 5, 1942 1,717,712 Loewe June 18, 1929 2,205,306 Olshevsky June 18, 1940 1,970,084 Feussner Aug. 14, 1934 1,765,413 Fruth June 24, 1930 2,021,661 Kisfaludy Nov. 19, 1935 1,339,505 Fahrenwald -..Ma.y 11, 1920 

